Steam boiler plants in which the combustion of the fuel necessary for the generation of steam takes place in a fluidized-bed are known. In the fluidized-bed, the fuel is mixed with an inert, grain-shaped material, which does not itself participate in the combustion. The inert material serves to maintain an even distribution of the fuel on the fluidized-bed and to transfer the heat generated to heat absorbers, e.g. built-in heat absorbing boiler tubes. Also, at least part of the oxygen necessary for the combustion is taken from the fluidizing air between the inert material.
However, in fluidized-beds the bottom on which the fluidized material rests is disadvantageously rather complex, inasmuch as it is composed of a number of nozzles through which the fluidizing air is blown in. Such nozzles are likely to block up, and it calls for a considerable pressure drop over the nozzles in order to maintain an even air flow over the entire cross-section of the bed. This in turn results in a substantial loss of power. I have invented an improved whirl chamber type boiler plant which avoids the above-noted limitations of the prior art.